1. Field of the Invention
This disclosure relates generally to cover systems, and, more particularly, cover systems that include fusion welds.
2. Description of Related art
Floating cover systems are used to cover storage ponds and the like for various purposes, such as reducing evaporation, controlling rainwater, preventing contamination, controlling odor, collecting gases, etc. FIG. 1 shows one example of a prior art cover system 10 for a storage basin 12. The perimeter of storage basin 12 is formed by an earthen berm 32. A liner 14 (which is typically a geomembrane material) is deployed into storage basin 12 and extends into an anchor trench 16. Anchor trench 16 is backfilled with filler material 18 to hold liner 14 in place. Cover 20 is placed on top of liner 14. The perimeter of cover 20 is welded to the perimeter of liner 14 using an extrusion welding process at a first weld 22. A cap strip 24 is extrusion welded to liner 14 and cover 20 using second and third extrusion welds 26, 28, respectively. The purpose of the cap strip is to provide: 1) a redundant gas tight seal; and 2) a redundant mechanical connection of the cover to the liner. To avoid leakage (no leaks at all are allowed in some instances), each of first, second, and third welds 22, 26 and 28 must be substantially continuous around the entire perimeter of cover 20. A corrugated pipe 30 may be laid around the perimeter of storage basin 12 to collect any gases that collect under cover 20.
The extrusion welding process used to weld cover 20 to liner 14 is a manual process that is labor intensive and dependent upon operator skill. To achieve good quality extrusion welds, cover 20 and liner 14 must be prepared correctly. They must be cleaned to remove any contamination, ground or scraped to remove oxidation, and properly aligned and tack welded together. If not prepared correctly, or if the operator is insufficiently skilled, the welds are subject to leaks and breakage. When such welds are constructed in place at the construction site, they are susceptible to contamination from debris, and dependent upon good weather conditions. One person can test several hundred linear feet of a fusion weld in about 10 minutes with an “Air Channel Test”. One person can only test about 2.5 linear feet per minute (25 linear feet/10 minutes), about 1/10th of the speed of fusion weld testing.